We finally got the update to the WPG2 plugin that makes it compatible with WordPress 2.1. After testing it on one site, I was able to update all my Gallery2 sites. So if you want to integrate your Gallery2 install with your WordPress 2.1 install, visit WPG2 and get the plugin.
WPG2 is a WordPress Plug-in that embeds Gallery2 within WordPress to share photos, videos and any other Gallery2 content seamlessly into the WordPress Sidebar and Blog entries.